U.S. Pat. No. 3,905,290, granted Sep. 16, 1975, to Robert A. Caughey, discloses a press which includes a reciprocating slat conveyor. The conveyor includes adjacent slat members which are in contact with the material to be conveyed. Linear hydraulic motors are used to move the slat members, in unison, in the conveying direction, and to move the floor members sequentially in the opposite direction. The control system for the linear hydraulic motors includes solenoid operated switching valves controlled by a rotary cam.
U.S. Pat. No. 3,146,678, granted Sep. 1, 1964, to Rudolf Paul Strick, discloses a system of three linear hydraulic motors which are moved in unison, in a first direction, and are moved sequentially in an opposite direction. The system utilizes a switching valve for switching hydraulic pressure and return between two conduits. The linear hydraulic motors include first and second working chambers on opposite sides of a piston head. The first conduit is connected to the first working chambers. The second conduit is connected to the second working chambers. The system includes sequence valves which function together to produce the desired movement of the motors.
The publication "Hydraulic Circuits And Control Systems", by J. R. Fawcett, published by the Trade And Technical Press Ltd., of Morden, Surrey England TJ843F35 (on pages 146 and 147) discloses an all hydraulic system for moving two or more linear fluid motors in unison, in a first direction, and moving them individually and in sequence, in the opposite direction. Circuit 75 includes a switching valve for switching hydraulic fluid pressure between two main conduits. One of the conduits extends to the first working chambers of the motors. The second conduit extends to the second working chambers of the motors. The system includes sequencing valves for effecting the sequential movement of the motors.
U.S. Pat. No. 4,143,760, granted Mar. 13, 1979, to Olof A. Hallstrom, discloses a reciprocating slat conveyor that is powered by hydraulic linear motors. The control system for the motors includes a switching valve that is biased into a first position by a spring and is moved into a second position by an air cylinder. Sequence valves in the form of internal check valves are provided in one of the conduits which is connected to the switching valve. This conduit extends in series through working chambers of the motors. Limit valves are provided to control the flow of air pressure into and out from the air cylinder which moves the switching valve.
Starting in about 1972, there has been a succession of reciprocating floor conveyor systems constructed which utilize two or more linear hydraulic motors for moving the conveyor slats in unison, in the conveying direction, and returning them one at a time back to a start position. Some of the control systems used included solenoid controlled valves and limit switches for energizing the solenoids. Other conveyor systems utilized a switching valve of the type disclosed by U.S. Pat. No. 3,530,895, granted Sep. 29, 1970, to Arthur A. Rothrock. Some of these systems combined with this switching valve internal check valves such as disclosed in U.S. Pat. No. 4,143,760. Others used sequence valves of the type disclosed in my aforementioned U.S. Pat. No. 4,748,893. Other systems utilized a switching valve of the type disclosed in my soon to issue application U.S. Ser. No. 07/659,843 filed Feb. 22, 1991, and entitled Poppet Valve And Valve Assemblies Utilizing Same, in combination with sequence valves generally of the type disclosed in my aforementioned U.S. Pat. No. 4,748,893.
There is a need for an all hydraulic control system for moving a plurality of linear hydraulic motors in unison, in a first direction, and moving them sequentially in the opposite direction, which utilizes a minimum of components and conduits which must be assembled and disassembled and which is reliable in operation and has a substantial use life. A principal object of the present invention is to provide a unique control system which meets these objectives.